Generation of Electric Power from a Thermal Spring

Characteristics of a Small-Size Screw Expander

Abstract

The performance characteristics of a small-size screw expander for the energy conversion of hot spring water are described in this report. Recently, the screw expander has been recognized as an effective machine for low temperature energy conversion, i.e. hot spring water. Usually in the low temperature energy conversion cycle, organic working mediums such as NH₃ or fron are used. With the organic working mediums, the performance tests of screw expander under the same conditions of a practical conversion cycle are very difficult. On the other hand, usually small-size screw expanders may be produced by adapting the massproduced screw compressors. We therefore made compression tests with air using small-size screw expanders. For a small-size screw expander, the compression tests with air are rather easy than the expansion tests with air or organic working mediums. If the performance of the expansion with organic working mediums could be estimated by the compression tests with air, it might be an effective technique for the design of the low temperature energy conversion cycle using the small-size screw expander. In this paper, we report the experimental results of the compression tests with air, of the expansion tests with air or RI 1, and comprise the results. The principal specifications of the two testing screw expanders are the built-in volume ratios are 2.0 and 2.4, and the exit displacement, 0.816m³/1000 rev., which is the same for both expanders.